1. Field of the Invention
The present invention relates to, for example, a semiconductor layer, a semiconductor device, a display device, a light-emitting device, a memory device, or a processor. The present invention relates to a method for manufacturing a semiconductor film, a semiconductor device, a display device, a light-emitting device, a memory device, or a processor. The present invention relates to a method for driving a semiconductor device, a display device, a light-emitting device, a memory device, or a processor.
Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A display device, a light-emitting device, a lighting device, an electro-optical device, a semiconductor circuit, and an electronic device include a semiconductor device in some cases.
2. Description of the Related Art
A technique for forming a transistor by using a semiconductor layer over a substrate having an insulating surface has attracted attention. The transistor is applied to a wide range of semiconductor devices such as an integrated circuit and a display device. A silicon layer is known as a semiconductor layer applicable to a transistor.
Whether an amorphous silicon layer or a polycrystalline silicon layer is used as a semiconductor layer in a transistor depends on the purpose. For example, in the case of a transistor included in a large display device, an amorphous silicon layer, which can be formed using an established technique for forming a film over a large substrate, is preferably used. On the other hand, in the case of a transistor included in a high-performance display device where driver circuits are formed over the same substrate, a polycrystalline silicon layer, which can form a transistor having a high field-effect mobility, is preferably used. As a method for forming a polycrystalline silicon layer, high-temperature heat treatment or laser light treatment which is performed on an amorphous silicon layer has been known.
In recent years, an oxide semiconductor layer has attracted attention. An oxide semiconductor layer can be formed by a sputtering method or the like, and thus can be used for a semiconductor layer of a transistor in a large display device. A transistor including an oxide semiconductor layer has a high field-effect mobility; therefore, a high-performance display device where driver circuits are formed over the same substrate can be obtained. Moreover, there is an advantage that capital investment can be reduced because part of production equipment for a transistor including an amorphous silicon layer can be retrofitted and utilized.
A transistor including an oxide semiconductor film is known to have extremely small leakage current in an off state. For example, a CPU with low power consumption utilizing the low leakage current of the transistor including an oxide semiconductor film is disclosed (see Patent Document 1).